A variety of systems are used in borehole geophysical exploration and production operations to determine chemical and physical parameters of materials in the borehole environs. The borehole environs include materials, such as fluids or formation matrix, in the vicinity of a borehole as well as materials, such as fluids, within the borehole. The various systems include, but are not limited to, formation testers and borehole fluid analysis systems conveyed within the borehole. In all of these systems, it is preferred to make all measurements in real-time and within instrumentation in the borehole. However, methods that collect data and fluids for later retrieval and processing are not precluded.
Formation tester systems are used in the oil and gas industry primarily to measure pressure and other reservoir parameters, such as permeability, of a formation penetrated by a borehole. Formation tester systems are also used to collect and analyze fluids drawn or flowed from the borehole environs and into a formation tester borehole instrument or “tool” to determine major constituents within the fluid. These parametric measurements are preferably made within the tool but can be combined with addition “in situ” or uphole analyses of physical and chemical properties of the formation fluid to evaluate hydrocarbon production prospects of a reservoir penetrated by the borehole. By definition, formation fluid refers to any and all fluid including any mixture drilling fluid and virgin formation fluids.
Regarding formation fluid sampling, it is of prime importance that fluid collected for analysis represents virgin formation fluid with little contamination from fluids used in the borehole drilling operation. Various techniques have been used to measure sample contamination including the monitoring of fluid pumped into the formation tester tool until one and/or more fluid properties, such as resistivity, cease to change as a function of time. These analyses are made within the formation tester tool in real time. Other techniques use multiple fluid input ports combined with borehole isolation elements such as packers and pad probes to minimize fluid contamination. Again, all fluid analyses are made within the formation tester tool or subsequently made at the surface of the earth.
Formation tester tools can be conveyed along the borehole by variety of means including, but not limited too, a single or multi-conductor wireline, a “slick” line, a drill string, a permanent completion string, or a string of coiled tubing. Formation tester tools may be designed for wireline usage or as part of a drill string. Tool response data and information as well as tool operational data can be transferred to and from the surface of the earth using wireline, coiled tubing and drill string telemetry systems. Alternately, tool response data and information can be stored in memory within the tool for subsequent retrieval at the surface of the earth.
Various methods are used to draw fluid into the formation tester tool for pressure measurements, analysis, sampling, and optionally for subsequent exhausting the fluid into the borehole. One method employs a radially extendable sampling pad that is pressed against the wall of the borehole. A pad fluid port or “snorkel” may or may not be extended from the center of the pad and through any borehole mud cake to make contact with formation material. Fluid is drawn into the formation tester tool via a flow line cooperating with the pad fluid port. Fluid properties are then measured within the formation tester and subsequently ejected back into the borehole or retained in one or more sample carrier chambers in the tester tool for return to the surface for subsequent analysis. A more detailed description of formation tester methodology is presented in U.S. Pat. No. 6,301,959 B1 and U.S. patent application Ser. No. 11/626,461 filed Jan. 24, 2007, both of which are here entered into this disclosure by reference.